Irritable Bowel Syndrome: What is Used to Make a Diagnosis?

Panelists share insight on what is included in a diagnostic work-up of irritable bowel syndrome (IBS).

Mark Pimentel, MD: I’ve been avoiding Dr Rezaie for a little while, because I’m going to slam him with a tough one. So for the work-up, what do you do? Do you do a colonoscopy? I guess this depends on age, right? If you have a 25-year-old woman in your office, what do you do? Versus a 50-year-old man or woman in your office coming with the same symptoms? We’re going to talk about all these things—colonoscopy, imaging, breath testing. Tell me what you do.

Ali Rezaie, MD: As Brennan mentioned, whenever there are features, that’s when we sometimes focus on the facts and conclude maybe something else is going on and assess the patient. For example, as you mentioned, if the age is more than 50 years and IBS [irritable bowel syndrome] starts, and that’s the time that we’re thinking, “OK, are we dealing with microscopic colitis? Is this a large polyp? Is this cancer?” That’s when we do a colonoscopy, for example. But as you said, if it’s a 25-year-old, otherwise healthy individual with IBS symptoms, that doesn’t necessarily warrant doing a colonoscopy.

The majority of these tests are designed to rule out other causes that can cause IBS-like symptoms. For example, stool test ruling out a Giardia [lamblia], for example. Or doing a colonoscopy for causes that I mentioned. Or doing a set of bloodwork or inflammatory markers to make sure that you’re not dealing with an inflammatory disease.

But there are other tests that are out there as well. For example, you mentioned breath testing. You can do breath testing for carbohydrate malabsorption, lactose intolerance. And other carbohydrate malabsorption can lead to symptoms that are similar to IBS as well, especially if you’re suspecting those on your history.

Mark Pimentel, MD: I know you had a recent study that suggests a breath test might predict response to drugs. Can you sum it all up?

Ali Rezaie, MD: Yes. That gets me to lactulose breath testing, which doesn’t necessarily diagnose irritable bowel syndrome. It’s used for a diagnosis of small-intestinal bacterial overgrowth. But there is an overlap between patients with IBS and small-intestinal bacterial overgrowth. In a study that Dr Lembo led, TARGET3, a subgroup of patients underwent some lactulose breath testing. And that showed that that can predict response to therapy for patients with IBS diarrhea to rifaximin, which is an interesting concept. We don’t have many determinants of response in IBS patients, and that was successful to do that.

Mark Pimentel, MD: A biomarker like that might be helpful to answer your question, Bill or Tony. If you can cultivate the patient who might respond, that might be a good thing to optimize, cost less, get the treatment faster. Tony, your thoughts on that?

Anthony J. Lembo, MD: No, I agree. I think that’s what we’re looking for: a biomarker that can predict outcome. I think it’s probably worth just stepping back for a second. If someone presents to my office with typical IBS, with diarrhea symptoms, in my mind I’m kind of thinking that it depends on the chronicity in the absence of new alarm features. But you still want to rule out a few basic things. I think we still want to make sure they don’t have celiac disease. It’s recommended that these patients have a tTG [tissue transglutamine] antibody, because occasionally you see it. It’s not very common. It’s probably less than 1%. But that is a different treatment algorithm if they have celiac disease. I’ll oftentimes check stool for ova and parasite, although extremely rarely. Sometimes these people have been traveling. I think that’s reasonable to do. And sometimes, in the back of my mind, I’m thinking the big differential is, clearly, do they have inflammatory bowel disease? And sometimes Crohn disease can present with a chronic diarrhea that’s intermittent with chronic pain. So there we’ll do inflammatory markers. And Bill has done a really nice study showing that if you have a low CRP [C-reactive protein], which is a serum test for inflammation, and a calprotectin, which is a stool marker for inflammation, then the odds of having inflammatory bowel disease is extremely unlikely. And what I see in our practice: a lot of these people are undergoing colonoscopies to exclude it when they don’t really need it. They’re 25 years old. They’ve had chronic diarrhea. With these tests you can exclude it. So that’s what I would do in a patient. We always do a CBC [complete blood count] in patients too. Some people would argue for maybe looking at their thyroid with a TSH [thyroid-stimulating hormone]. That’s pretty much the game. So there’s not an extensive array of tests in most patients.

Mark Pimentel, MD: There is a new blood test that helps diagnose postinfectious IBS. Do you have any thoughts of where that could play a role in IBS?

Anthony J. Lembo, MD: Sure. So this test looks at antibodies to anti-vinculin and anti-CdtB [cytolethal distending toxin B]. So it really looks for infections. In patients, infections are probably the most common cause for IBS. This test has shown that if you have a positive test, the odds that you have IBS are extremely high—in the mid to upper 90% range. You can rule in IBS with diarrhea in those patients. I think for a person who is uncomfortable with the diagnosis, this may play a role and can reduce further testing for them.